Structure of the Tandem MA-3 Region of Pdcd4 Protein and Characterization of Its Interactions with eIF4A and eIF4G

Abstract

One of the key regulatory points of translation initiation is recruitment of the 43S preinitation complex to the 5′ mRNA cap by the eIF4F complex (eIF4A, eIF4E, and eIF4G). The tumor suppressor protein Pdcd4 has been shown to inhibit cap-dependent translation by interacting tightly with the RNA helicase eIF4A via its tandem MA-3 domains. The NMR studies reported here reveal a fairly extensive and well defined interface between the two MA-3 domains in solution, which appears to be stabilized by a network of interdomain salt bridges and hydrogen bonds, and reveals a unique orientation of the two domains. Characterization of the stoichiometry of the Pdcd4-eIF4A complex suggests that under physiological conditions Pdcd4 binds to a single molecule of eIF4A, which involves contacts with both Pdcd4 MA-3 domains. We also show that contacts mediated by a conserved acidic patch on the middle MA-3 domain of Pdcd4 are essential for forming a tight complex with eIF4A in vivo, whereas the equivalent region of the C-terminal MA-3 domain appears to have no role in complex formation in vivo. The formation of a 1:1 eIF4A-Pdcd4 complex in solution is consistent with the reported presence in vivo of only one molecule of eIF4A in the eIF4F complex. Pdcd4 has also been reported to interact directly with the middle region of eIF4G, however, we were unable to obtain any evidence for even a weak, transient direct interaction.

Regulatory Effects of Programmed Cell Death 4 (PDCD4) Protein in Interferon (IFN)-Stimulated Gene Expression and Generation of Type I IFN Responses

“…This protein interacts with eIF4A (25,48,53,55) and negatively controls the helicase activity of eIF4A and cap-dependent translation (37,48,55). Notably, beyond free eIF4A, PDCD4 inhibits the function of eIF4F-bound eIF4A (24,53,55), providing a mechanism by which it may be acting as a suppressor of mRNA translation (48,55). There is also evidence that PDCD4 binds RNA and interacts with eIF4G in vitro (2,48,55).…”

“…PDCD4, a tumor suppressor protein for which the human gene is located on chromosome band 10q24 (46), has important regulatory functions in mammalian cells (4,14,24,25,33,54,56). This protein interacts with eIF4A (25,48,53,55) and negatively controls the helicase activity of eIF4A and cap-dependent translation (37,48,55). Notably, beyond free eIF4A, PDCD4 inhibits the function of eIF4F-bound eIF4A (24,53,55), providing a mechanism by which it may be acting as a suppressor of mRNA translation (48,55).…”

“…There is extensive previous work demonstrating that PDCD4 is a tumor suppressor (4,12,53) and that its expression is decreased in several malignancies (11,12,14,31,33,44,53). PDCD4 has also been shown to regulate cell cycle progression in a cell-type-specific manner and to inhibit cell proliferation (13).…”

Pdcd4 directly binds the coding region of c-myb mRNA and suppresses its translation

“…As a translation regulator, Pdcd4 interacts with the eukaryotic translation initiation factor eIF4A, a RNA helicase that catalyzes the unwinding of mRNA secondary structures in 5 0 -untranslated regions (UTRs) (Yang et al, 2003a(Yang et al, , 2004. Binding of Pdcd4 to eIF4A is mediated by the MA-3 domains, whose structure and complex formation with eIF4A have been analyzed in detail (LaRondeLeBlanc et al, 2007;Waters et al, 2007Waters et al, , 2011Suzuki et al, 2008;Chang et al, 2009;Loh et al, 2009). Because binding of Pdcd4 to eIF4A inhibits the helicase activity of eIF4A (Yang et al, 2003a;Yang et al, 2004), it is believed that Pdcd4 functions as a suppressor of cap-dependent translation of mRNAs with structured 5 0 -UTRs.…”

Dicer1 imparts essential survival cues in Notch-driven T-ALL via miR-21–mediated tumor suppressor Pdcd4 repression

“…Pdcd4 was sufficient to induce apoptosis in T-ALL cells, suggesting that apoptosis of T-ALL cells in which miR-21 expression is downregulated is at least partly caused by derepression of Pdcd4. Recent structural studies on PDCD4 revealed that it inhibits initiation of cap-dependent protein translation by binding to the RNA helicase elongation initiation factor 4A (eIF4A) and the scaffold protein elF4G 65 or by blocking internal ribosomal entry site-mediated translation of the prosurvival genes Bcl-XL and Xiap. 42 Interestingly, our correlative studies on BCL-xL protein levels in murine and human T-ALL cell lines confirms that miR-21 is regulating BCL-xL through the repression of Pdcd4.…”